Deposition of Gan Films Using Seeded Supersonic Jets
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Mat. Res. Soc. Symp. Proc. Vol. 388 01995 Materials Research Society
probability of hydrides, such as Si 2H 6 , SiH 4 , NH 3 and CH 4 , is relevant to the growth of wide bandgap semiconductors. In this paper, we report initial results on the use of a seeded supersonic jet to produce suprathermal NH 3 molecules for GaN deposition on sapphire. TEG was chosen as the Ga precursor, since it decomposes at low temperature via P-hydride elimination with negligible codeposition of carbon. The deposited films were characterized by Auger electron spectroscopy (AES), X-ray diffraction (XRD), reflection high-energy electron diffraction (RHEED) and scanning electron microscopy (SEM). EXPERIMENTAL METHODS The supersonic jet deposition apparatus comprises a two-compartment vacuum chamber, a heated nozzle assembly (for NH 3/He), an unheated tubular nozzle (for TEG/He), a gas delivery system, and a substrate heater assembly. The 10-in. cylindrical chamber is divided into two compartments by a removable skimmer plate. The source chamber is pumped by a CVC PVMS6 diffusion pump backed by a Tuthill 3206 Roots blower and a Welch 1374 mechanical pump with a liquid nitrogen cold trap. The deposition chamber is pumped by a Varian VHS-6 diffusion pump backed by a Varian 2033 mechanical pump with a liquid-nitrogen-cooled baffle. The base pressure in each chamber is less than 3x10- 7 Torr. In the experiments described herein, the skimmer plate was removed, allowing the heated nozzle to be placed within 1 in. of the substrate. The heated nozzle assembly was fabricated from a 1-in. O.D. high-pressure filter body (HiP, Pittsburgh). A thin Pt disk containing a 200-l.tm laser-drilled pinhole (Energy Beam Sciences) is mechanically sealed to a short piece of 1/8-in. OD tubing which protrudes from one end of the filter body. The disk is centered and compressed by a threaded cap with a 1-mm exit aperture. The nozzle assembly is sheathed by a 275-W annular nozzle heater (Chromalox HBA103027, inner diameter: 1 in., length: 3 in., and max. attainable temperature: 600'C). The unheated tubular nozzle was constructed from 1/8-in. OD high-pressure tubing with an inner diameter of approximately 0.4 mm. The pressure in the heated nozzle is controlled by a multi-channel flow/pressure controller (MKS 647) using pressure feedback from a capacitance manometer. The NH 3 and He flow rates are regulated by MKS 1259 mass flow controllers (MFCs); in operation, the NH3: He flow ratio is fixed, and the total flow rate is adjusted to maintain a pressure setpoint. The He flow rate through the metal-organic bubbler is controlled using an MFC. The bubbler is immersed in a constant-temperature bath, and the bubbler pressure is controlled by a downstream needle valve and monitored by capacitance manometer. As TEG is pyrophoric, the process effluent is passed through a canister scrubber (Novapure). The substrate heater assembly is mounted on a rotary-linear feedthrough which is positioned along the centerline of the deposition chamber. The substrate is heated from the backside b
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